1. Field of the Invention
The present invention relates to a liquid crystal display element including a nematic liquid crystal dispersed and held in a solidified matrix, especially, a liquid crystal display element having an active element for each picture element electrode and a projection type liquid crystal display apparatus using such display element.
In recent years, liquid crystal displays have been widely used for personal word processors, hand-held computers portable TV sets and so on, taking the advantages of low power consumption, low driving voltage and so on. Of the liquid crystal displays, liquid crystal display elements having an active element for each picture element electrode have particularly been noted and developed.
As such liquid crystal display elements, there was a proposal on liquid crystal display elements in which a dynamic scattering mode (DSM) liquid crystal is used. However, the liquid crystal display element of this type had a disadvantage of large current consumption because a high value of electric current passed in the DSM liquid crystal. Now, liquid crystal display elements in which a twist nematic (TN) type liquid crystal is used have been widely used. For instance, portable TVs have been widely commercialized. Since the TN type liquid crystal display element has a very small leak current and a small power consumption, it is suitable for using a battery as a power source.
When the liquid crystal display element using active elements is used for DS mode, the leak current of the liquid crystal itself is large. Accordingly, it was necessary to provide a large storage capacitance in parallel to each picture element, and the power consumption of the liquid crystal display element itself is large.
In the TN mode, since a leak current in the liquid crystal itself is very small, it is unnecessary to provide a large storage capacitance and the power consumption of the liquid crystal display element itself can be small.
In the TN mode liquid crystal, however, there is a problem that the transmittance of light is small because two polarization plates are required. In particular, when a color filter is used for obtaining a colored display, only several percents of incident light can be utilized. It is, therefore, necessary to use a strong light source, as a result of increasing power consumption.
Further, the TN mode liquid crystal display element has disadvantages of requiring a very strong light source for projecting a picture image on a projection screen, difficulty in obtaining a high contrast on the projection screen, difficulty in obtaining a high contrast on the projection screen, and adverse effect to the liquid crystal display element due to heat from the light source.
In order to solve the problems in the TN mode liquid crystal display element, there is proposed such mode that a liquid crystal polymer composite material in which a nematic liquid crystal is dispersed and held in a polymer matrix is used, and a low voltage such as 10 V or lower is sufficient to drive it by utilizing the scattering-transparent characteristics.
However, in the conventional liquid crystal and polymer composite material, there was hysteresis in the voltage-transmittance characteristics, that is, there was a problem that the transmittance during the increase of voltage is different from that during the decrease of voltage. Accordingly, there was a problem of a phenomenon of image-sticking wherein a picture image which had appeared in the display just before the changing of picture remained in the present display for several minutes.